This invention relates to video display units, in particular computer displays/monitors.
In order to minimise power consumption of desktop computers, a display power management signalling (DPMS) standard has been defined by VESA (Video Electronics Standards Association). This aims to provide a common definition and methodology in which the display controller sends a signal to the display that enables it to enter various power management states. Four states are defined, xe2x80x9cONxe2x80x9d, xe2x80x9cSTAND-BYxe2x80x9d, xe2x80x9cSUSPENDxe2x80x9d and xe2x80x9cOFFxe2x80x9d. xe2x80x9cONxe2x80x9d refers to the state of a display when it is in full operation. xe2x80x9cSTAND-BYxe2x80x9d is an operating state of minimal power reduction and with the shortest recovery time. xe2x80x9cSUSPENDxe2x80x9d refers to a level of power management in which a substantial power reduction is achieved by the display. A longer recovery time from this state is permitted than from the Stand-by state. xe2x80x9cOFFxe2x80x9d indicates that the display is consuming the lowest level of power and is non-operational. Normally a monitor in the DPMS OFF state consumes a few watts, typically 3-5W. This consumption is necessary for xe2x80x9cwatchingxe2x80x9d the sync signals and to make automatic xe2x80x9cwake-upxe2x80x9d possible. The present invention is, however, aimed at providing means whereby the power consumption in the DPMS OFF mode is reduced to almost zero, but the display can still be xe2x80x9cwoken upxe2x80x9d from this mode when the sync pulses are reapplied, this being achieved in a manner which is such that a number of somewhat contradictory requirements are fulfilled. The requirements are
(i) that the sync inputs must be fully TTL-compatible, in order to ensure no overloading,
(ii) that there is full DPMS compatibility ie must wake up even if just one of the sync signals is active, with a worst-case duty cycle and polarity and
(iii) that this is achieved at moderate cost.
In GB 2264848 (ICL Personal Systems Oy) there is described a video display with remote power switching. The video display unit has a built-in power supply and at least one electrically controllable power switch for connecting mains voltage to the power supply. A control circuit closes and opens the power switch, for switching on and off the display unit, in response to the state of at least one video or deflection signal received by the display unit, or a command received via a communications channel utilising the signals of the video interface. By this means it is possible to automatically switch on the display unit at the same time as the control unit (processor) is started. In GB 2264848 this is achieved by rectifying at least one video or deflection signal, charging a capacitor with the rectified signal and generating a start-up current pulse from the capacitor. The pulse is supplied to the power switch, which when closed connects mains power to the power supply. In other words, power for the switching is taken from the sync signals, rectified, voltage doubled and applied to solid state relays comprising the switch. Whilst this is simple in principle there are difficulties associated with it. If the duty cycle of the syncs is low, the voltage doubler will take a long time to charge. The solid state relays need to be very sensitive and in any event they are expensive.
In EP A2 0709764, there is disclosed a power supply system, including a source control circuit for operating a CRT display unit, which is capable of reducing power consumption during an interruption of an external input signal given to the power supply system. A holding circuit of a power control circuit is operable in response to such an interruption to de-energise the source control circuit and is put into a self-holding state to maintain a stop mode of the source control circuit, until the external input signal is received again. The circuitry described enables the electric power to be reduced to the order of 5 watts.
In DE A1 195 25 439, there is disclosed another energy-saving circuit for a display apparatus, which controls turn on and/or off of an AC voltage supply and without the need for an auxiliary power supply. This arrangement is such that the electric power is reduced to below 1 watt.
The present invention aims to achieve automatic awakening from the DPMS OFF mode in an alternative and cost-advantageous manner, and which permits almost zero power consumption in that mode.
According to the present invention there is provided a video display unit comprising a built-in power supply including electronically-controllable switch means, and control means responsive to the presence of at least one active video or deflection signal received by the display unit to switch on the display unit by appropriate control of the switch means, the switch means being controlled in response to power extracted from the at least one active signal, and the control means including peak sensing circuits for extracting power from the at least one signal, said peak sensing circuits comprising a respective diode/capacitor combination for each video or deflection signal, and ac sensing circuits for detecting if the at least one signal is active or not, characterised in that the ac sensing circuits comprise a respective capacitor/diodes combination for each video or deflection signal.